* #11371 Remove GLEW dependency and use Qt's QOpenGLFunctions
Replace embedded GLEW library with Qt's native OpenGL function loading
(QOpenGLFunctions/QOpenGLExtraFunctions) to resolve Qt 6 compatibility
warnings about GLEW conflicts with qopenglfunctions.h.
- Update CVF_CALLSITE_OPENGL macro to provide QOpenGLExtraFunctions pointer
- Replace GLEW initialization with Qt OpenGL context validation
- Keep direct calls for fixed-function GL (glBegin, glEnd, glMatrixMode, etc.)
- Remove glew/ directory containing embedded GLEW source
* #11371 Remove GLU dependency to fix Windows build error
GL/glu.h conflicts with Qt's OpenGL headers on Windows due to APIENTRY
redefinition. Replace gluBuild2DMipmaps with glTexImage2D + glGenerateMipmap,
and gluOrtho2D with glOrtho.
Kristian Bendiksen
sigurdp